Control systems for internal combustion engines include a plurality of sensors whose signals are evaluated for the engine control in combination with the load detection. The typical sensors include an air mass sensor for measuring the air mass flow, which is supplied to the engine, an ambient air pressure sensor for measuring the ambient pressure of the internal combustion engine (atmospheric pressure), sensors for measuring the throttle flap angle in combination with a throttle positioning device as well as, if needed, a sensor for measuring the intake air temperature. The signals of these sensors are used for determining the engine load which, in turn, is essential for the formation of actuating quantities. For this reason, these signals have an influence on the mixture formation and the exhaust-gas composition. A monitoring of the correct function of these sensors is therefore necessary with a view to the increasing requirements imposed on the exhaust-gas composition.
For example, DE-A 40 04 085 (U.S. Pat. No. 5,260,877) shows, in combination with the detection of the throttle flap angle, the use of two mutually redundant sensors for detecting the throttle flap angle. A fault function of one of the sensors is derived from the signals by way of a comparison of these signals to each other.
For monitoring an air mass sensor, DE-A 195 13 370 (U.S. Pat. No. 5,755,201) describes a procedure wherein a fault is assumed in the region of the air mass sensor when the output signal of a lambda controller exceeds a pregiven limit value, that is, when an excessive correction of the mixture formation by the lambda controller is detected.
A further procedure for monitoring the operation of the air mass sensor is described in DE-A 197 40 918. Here, the air mass flow via the throttle flap is determined on the basis of model quantities and measurement quantities in dependence upon the detected throttle flap angle and is compared to the air mass flow measured by the air mass sensor. At least one corrective factor is formed in dependence upon the deviation between the two quantities. The magnitude of this corrective factor can be applied as an index for faults in the region of the air mass detection via the air mass sensor and/or in the region of the air mass detection with respect to the throttle flap angle.
An air mass flow signal is measured in DE 197 50 191 A1 and a further air mass flow signal is computed on the basis of a throttle flap position signal. The two signals are matched to each other. For fault monitoring, the matched signals are compared to each other and a fault is detected when the two signals deviate impermissibly from each other. A torque reduction and a fault separation is undertaken when faults are detected.
Depending upon the embodiment, the signal value of the ambient pressure sensor is significant, for example, in the described matching or for the adjustment of the throttle flap of the internal combustion. For this reason, there is also the need for a fault detection of this sensor.
The monitoring of an ambient pressure sensor is known from the non-published German patent application DE 100 21 639.0 of May 4, 2000. There, in the unthrottled operation of the internal combustion engine (that is, for an opened throttle flap), the signal of the ambient pressure sensor is compared to a computed intake manifold pressure value. A malfunction is assumed when there is an impermissible deviation of these two values.